Besides larger fuel injectors, fuel pump, and a tune, what else is needed to run E85 (E54 in Arizona)? Just wondering since I know ethanol is very corrosive. I was also considering going the flex fuel route for convenience.

Correct, larger fuel injectors and a compatible E85 fuel pump, unless your making big power the stock plastic fuel lines will Suffice, I would upgrade the fuel filter for one that also is compatible and better flow rate, as for the injector O rings, I've been running on E85 for 4 years now with no issues, but when I store the vehicles I usually fill up with 93 pump, as E 85 will hold moisture.
Have a tuner that knows E85 tunes and get your self a E 85 fuel tester, I always check my fuel as if the E 85, it changes in winter months(E75) and doesn't usually switch back till early April.

Get your self a flip chip with the ability to hold several tunes, this way its easy as changing the fuel and flipping the switch.

Correct, larger fuel injectors and a compatible E85 fuel pump, unless your making big power the stock plastic fuel lines will Suffice, I would upgrade the fuel filter for one that also is compatible and better flow rate, as for the injector O rings, I've been running on E85 for 4 years now with no issues, but when I store the vehicles I usually fill up with 93 pump, as E 85 will hold moisture.
Have a tuner that knows E85 tunes and get your self a E 85 fuel tester, I always check my fuel as if the E 85, it changes in winter months(E75) and doesn't usually switch back till early April.

Get your self a flip chip with the ability to hold several tunes, this way its easy as changing the fuel and flipping the switch.

My GT car makes 704 WRHP on the Corn vs 635 RWHP 93 pump

Yeah, the plan is to replace stock injectors with 60 lbs injectors, get a DeatschWerks 340 LPH fuel pump, and upgrade fuel lines. Unfortunately, there's only E54 in Arizona (no E85). Still better than 91/93 pump gas though as far as power gains. Ideally, I would like to go the flex fuel tune route, so I don't have to worry about ethanol %. Just have to find a tuner who knows a lot of flex fuel tunes on 4.6 DOHC Mustangs. Also, have plans to install a Hellion Single Turbo setup (67mm Precision, ball bearing) by the end of the year.